arch: Atmel SAM E70: remove now redundant IRQ id defines

same70/soc.h provided IRQ ids as #define. This is no longer
necessary as gen_isr_tables mechanism, which was recently
introduced, supports IRQ ids as enums. These are provided
directly by Atmel ASF library.

Change-Id: I3c2573d97d81eb9a02e85fde0566622ff2ecf2cf
Signed-off-by: Piotr Mienkowski <piotr.mienkowski@gmail.com>